Power steering device

ABSTRACT

A power steering apparatus includes: a steering load average value calculating circuit  39  which calculates a steering torque average value Trav which is the average value of steering torque Tr within a predetermined interval of time; and an abnormality detection circuit  40  which compares steering torque average value Trav with a specified steering torque value Trrf and detects the abnormality of the apparatus when steering torque average value Trav is larger than the specified value.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S.application Ser. No. 15/623,936, filed Jun. 15, 2017, which is acontinuation application of U.S. application Ser. No. 14/768,653, filedAug. 18, 2015, which is a U.S. National Stage Application ofPCT/JP2014/050987, filed on Jan. 20, 2014, which claims the benefit ofpriority from Japanese Patent Application No. 2013-058878, filed Mar.21, 2013; the entire contents of all of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a power steering apparatus applicable,for example, to an automotive vehicle.

BACKGROUND ART

A power steering apparatus of this kind is known from a Patent Document1.

In a technique described in this Patent Document 1, a water dropletsensor is installed at an inner periphery of a gear housing terminal.When this water droplet sensor detects a water droplet adhered to a rackbar, a vehicle driver is informed that an abnormality is generated inthe power steering apparatus.

PRE-PUBLISHED DOCUMENT Patent Document

Patent Document 1: A Japanese Patent Application First Publication(tokkai): No. 2006-111032.

DISCLOSURE OF THE INVENTION Task to be Solved by the Invention

However, in the above-described conventional power steering apparatus,an abnormality detection is based on a water invasion. Hence, anothermember (the above-described water droplet sensor) than components of theapparatus is installed. Thus, a cost increase of the apparatus cannot beavoided.

In addition, even in a case where the water droplet is adhered onto arack shaft, there are often cases where a serious inconvenience based ona rust developed due to the water droplet such as a fixation of the rackshaft is not introduced. Hence, when the water droplet is detected, theconventional apparatus immediately determines an occurrence of theabnormality. At this time, there is a possibility that a replacement ofthe component (or the replacement of the whole apparatus) not alwaysrequired is carried out.

It is, with the above-described task in mind, an object of the presentinvention to provide a power steering apparatus which is capable ofdetecting only the abnormality required for the apparatus withoutincrease of the cost.

Means for Solving the Task

According to the present invention, the power steering apparatuscomprises: a steering load average value calculating circuit thatcalculates an average value of a steering load corresponding value whichis, especially, any one of a steering torque within a predeterminedinterval of time, a motor command current which is drivingly controllingan electrically driven motor, and a motor actual current which isactually flowing through the electrically driven motor; and anabnormality detection circuit which compares the average value of thesteering load corresponding value with a specified value stored in acontrol unit to detect an abnormality of the apparatus when the averagevalue is larger than the specified value.

Effect of the Invention

According to the present invention, a state in which the average valueintroduced from the existing structure of the apparatus is larger thanthe specified value is defined as an abnormality and the abnormalitydetection is carried out. It becomes possible to detect a progressdegree of the rust developed in the steering mechanism with the steeringload of the apparatus. Thus, a required abnormality only can be detectedwithout use of another member.

That is to say, even if the rust is developed in the steering mechanism,a serious inconvenience such as the fixation of the steering mechanismis not immediately generated. The steering load is increased togetherwith the progress degree of rust and, as its final stage, the seriousinconvenience such as the fixation of the steering mechanism isgenerated. Thus, it becomes possible to detect a really dangerousabnormality only for the apparatus by detecting the steering load whichis increased together with the progress degree of rust as describedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a rough configuration view of a power steering apparatusaccording to the present invention.

FIG. 2 is an arrow marked view of the power steering apparatus viewedfrom an A direction shown in FIG. 1.

FIG. 3 is a cross sectional view cut away along a line B-B in FIG. 2.

FIG. 4 is a control block diagram of an ECU shown in FIG. 1 representinga first preferred embodiment of the power steering apparatus accordingto the present invention.

FIG. 5 is a flowchart representing a control flow of a rust detectingsection in FIG. 4.

FIG. 6 is a flowchart representing a detail of an averaging process inFIG. 5.

FIG. 7 is a flowchart representing a control of FIG. 5 with a steeringangle and a steering speed taken into consideration.

FIG. 8 is a flowchart representing a control of FIG. 7 with adetermination of bumping of a steering wheel added.

FIG. 9 is a flowchart representing a control of FIG. 5 with a steeringangle and a yaw taken into consideration.

FIG. 10 is a flowchart representing a control of FIG. 5 with a roadwheel speed taken into consideration.

FIG. 11 is a flowchart representing a control of FIG. 5 with an averagevalue immediately before an ignition (switch) off at a previous timetaken into consideration.

FIG. 12 is a flowchart representing a detail of an averaging process ofFIG. 10.

FIG. 13 is a flowchart representing the averaging process of FIG. 12with a weighting added.

FIG. 14 is a flowchart representing a control of FIG. 5 with a gradualreducing process of a motor command current added

FIG. 15 is a control block diagram of an ECU shown in FIG. 1representing a second preferred embodiment of the power steeringapparatus according to the present invention.

FIG. 16 is a flowchart representing a control flow of the rust detectingsection in FIG. 15.

FIG. 17 is a flowchart representing a control of FIG. 16 with a processin accordance with a number of an abnormality frequency added.

FIG. 18 is a flowchart representing a control of FIG. 16 with a motorcommand current used in place of a steering torque in the control ofFIG. 16.

FIG. 19 is a map view representing a detail of an abnormality range MAP1shown in FIG. 18.

FIG. 20 is a flowchart representing a control of FIG. 16 with a motoractual current used as a replacement of the steering torque.

FIG. 21 is a view representing a detail of an abnormality range MAP2 inFIG. 21.

EMBODIMENTS FOR CARRYING OUT THE INVENTION First Embodiment

Hereinafter, preferred embodiments of a power steering apparatusaccording to the present invention will be described on a basis of thedrawings.

As shown in FIGS. 1 through 3, a steering wheel 1 disposed within adriver's cab of a vehicle and steerable wheels 2, 3 which are frontright and left road wheels are mechanically linked together by means ofa steering mechanism. This steering mechanism includes: a steering shaft6 integrally rotatably linked via an intermediate shaft 4 and universaljoint 5; a pinion shaft 7 made of a steel material and linked tosteering shaft 6 via a torsion bar (not shown); and a rack bar 8 made ofthe steel material and on an outer periphery of which a rack 8A meshedwith a pinion 7A is installed at the outer periphery of pinion shaft 7.Both terminal sections of rack bar 8 are linked to the correspondingsteerable wheels 2, 3 via ball joints 9, 10, tie rods 11, 12, knucklearms 13, 14, and so forth.

In such a construction as described above, when the driver makes apivotal operation of steering wheel 1, intermediate shaft 4 and steeringshaft 6 are accordingly revolved around their axes so that the torsionbar is twisted. An elastic force of the torsion bar generated therebycauses pinion shaft 7 to be revolved following steering shaft 6. Thus,the rotational movement of pinion shaft 7 is converted into a linearmovement along an axial direction of rack bar 8 by means of the rack andpinion mechanism described above. A direction of steerable wheels 2, 3is modified by knuckle arms 13, 14 being pulled toward a vehicular widthdirection via ball joints 9, 10 and tie rods 11, 12.

In a sensor housing 16 enclosing peripheries of steering shaft 6 andpinion shaft 7, as sensor members to detect various kinds of steeringinformation, a steering angle sensor 17 for detecting a steering angleof steering shaft 6 (FIG. 4) and a torque sensor 23 for detecting asteering torque inputted to steering shaft 6 on a basis of a relativerevolution angular difference between steering shaft 6 and pinion shaft7 due to a twist of the torsion bar (FIG. 4) are housed.

Furthermore, bellows shaped boots 25, 26 are disposed across an outerperiphery of one end side of tie rods 11, 12 at axial both ends of gearhousing 24 enclosing the periphery of rack bar 8. These boots 25, 26 areformed so as to secure a predetermined flexibilities by means of, forexample, a synthetic rubber material or so forth and these boots 25, 26prevent invasions of water, dust, and so forth into rack bar 8 and aball-screw mechanism 27 which will be described later.

An electrically driven motor 19 is linked with rack bar 8 by connectingan input pulley 21 fixed to an outer periphery of a tip of an outputshaft 20 of motor 19 to an output pulley 22 fixed to the outer peripheryof rack bar 8 via a belt 15. It should be noted that both pulleys 21, 22and belt 15 constitute a transmission mechanism. Then, a ball-screwmechanism 27 which is a speed reduction mechanism and having a spirallywound groove shape is interposed between pulley 22 and rack bar 8.

Above-described ball-screw mechanism 27 is constituted by: a rack barside ball screw groove 8A installed on an outer peripheral side of rackbar 8 and having a spiral groove shape; a nut 44 annularly installed soas to enclose rack bar 8 and rotatably disposed with respect to rack bar8; a nut side ball screw groove 44A, installed on an inner peripheralside of nut 44, having a spiral groove shape, and constituting a ballcirculation groove 45 together with rack bar side ball screw groove 8A;a plurality of metallic balls 28 installed within ball circulationgroove 45; and a tube (a circulation member) made of an iron-seriesmetal (not shown) connecting between one end side of ball circulationgroove 45 so that ball 28 can be circulated from one end side of ballcirculation groove 45 to the other end side. The revolution ofelectrically driven motor 19 transmitted via belt 15 is speed reducedand converted to the linear motion of rack bar 8.

A control unit (ECU) 18 is integrally constituted by electrically drivenmotor 19, has a function storing and executing various kinds of controlprocesses and drivingly controls electrically driven motor 19 whichprovides a steering assistance torque for the steering mechanism on abasis of the steering information of the steering angle, the steeringtorque, a vehicle speed, and so forth.

A specific control structure of control unit 18 will be described indetails on a basis of FIG. 4.

FIG. 4 shows a control block diagram representing details of the controlstructure of control unit 18.

Control unit 18 (ECU) includes: an assistance current command section 30which calculates a drive current Io driving electrically driven motor 19on a basis of a steering torque Tr signal (hereinafter, referred to as asteering torque Tr) which is a signal of the steering torque detected bytorque sensor 23, a vehicle speed signal Vs (hereinafter, referred to asa vehicle speed Vs) detected by a vehicle speed sensor 29, for example,installed on a differential gear (not shown), and so forth and outputsthis drive current to electrically driven motor 19 side; and anabnormality detection command section 31 which detects an abnormality inthe power steering apparatus on a basis of steering torque Tr and soforth and controls assistance current command section 30 and so forth.

Assistance current command section 30 is constituted by: an assistancecurrent calculating section 32 which calculates a motor command currentTRr which drivingly controls electrically driven motor 19 on a basis ofvehicle speed Vs, a steering angle signal θ ang (hereinafter, referredto as “steering angle θ ang”), and steering torque Tr; a motor controlsection 33 which generates motor drive signal D for electrically drivenmotor 19 on a basis of motor command current TRr; and a motor drivesection 34 which supplies motor drive current Io for electrically drivenmotor 19 in accordance with motor drive signal D. A motor currentdetecting section 35 interposed between motor drive section 34 andelectrically driven motor 19 serves to feedback a motor actual currentIr actually flowing through electrically driven motor 19 to motorcontrol section 33.

It should be noted that each of steering torque Tr, motor commandcurrent TRr, and motor actual current Ir corresponds to a steering loadcorresponding value described in claims.

Abnormality detection command section 31 includes: a rust detectionsection 36; an alarm command section 37 which performs an alarm displayfor a warning lamp (not shown) in accordance with the process of rustdetection section 36; and a power supply interrupting section 38 whichinterrupts a power supply of electrically driven motor 19 in accordancewith the process in rust detection section 36. Abnormality detectioncommand section 31 detects the abnormality based on the generation ofrust in rack bar 8 and ball-screw mechanism 27 and informs the driver ofthe abnormality to pay the attention.

Rust detection section 36 includes: a steering load average valuecalculating circuit 39 which inputs steering torque Tr and calculates anaverage value of the steering torque for a predetermined interval oftime; and an abnormality detection circuit 40 which determines apresence or absence of the abnormality in accordance with a calculationresult of the steering load average value calculating circuit 39.

Steering load average value calculating circuit 39 and abnormalitydetection circuit 40 input, in addition to steering torque Tr, vehiclespeed Vs, steering angle θ ang, a yaw rate signal Yw detected by a yawrate sensor 41 installed, for example, on a weight center section of thevehicle (hereinafter, abbreviated as “yaw Yw”), a right road wheel speedsignal Vwr which is a right road wheel speed signal detected by a rightroad wheel speed sensor 42 installed on steerable wheel 2 (hereinafter,abbreviated as “right road wheel speed Vwr”), and a left road wheelspeed signal Vwl which is the left road wheel speed signal detected byleft road wheel speed sensor 43 installed on steerable wheel 3(hereinafter, abbreviated as “left road wheel speed Vwl”). Each of thesesignal values is provided for the abnormality determination inabnormality detection circuit 40.

In addition, abnormality detection circuit 40 compares the average valuewith each specified value previously stored in a non-volatile memory ofECU (not shown) and determines the presence or absence of theabnormality in accordance with the compared result and outputs apredetermined command to alarm command section 37, power supplyinterrupting section 38, and assistance current calculating section 32.

Hereinafter, control contents of rust detection section 36 willspecifically be explained on a basis of FIGS. 5 through 14.

FIG. 5 shows a flowchart representing a control flow of rust detectionsection 36.

That is to say, rust detection section 36, at first, determines whether“1” is inputted to an abnormality settlement flag Flerr, namely,determines whether the abnormality is already detected at a previousprocess (a step S101). If Flerr is “1” (the power supply to electricallydriven motor 19 is interrupted), the flow of FIG. 5 is ended. On theother hand, if Flerr is “0” (the power supply of electrically drivenmotor 19 is not interrupted), rust detection section 36 reads thesteering torque from torque sensor 23 (a step S102) and, then,calculates a steering torque average value Trav as the steering loadaverage value by an averaging process (the detail will be describedlater) of an absolute value of the steering torque Tr (a step S103),and, thereafter, reads a specified steering torque value Trrf previouslystored in the non-volatile memory (a step S104). It should be noted thatspecified steering torque value Trrf denotes steering torque Tr in thenormal state and corresponds to a specified value in the claims.

Then, rust detection section 36 determines a magnitude of steeringtorque average value Trav with respect to a value of specified steeringtorque value Trrf multiplied by 1.2 (a step S105). In a case wheresteering torque average value Trav is smaller than the value multipliedby 1.2 times specified steering torque value Trrf, namely, if arelationship of “Trav<1.2 Trrf” is established, rust detection section36 determines that no abnormality is found and the control flow isended.

On the other hand, if steering torque average value Trav is equal to orlarger than specified steering torque value Trrf multiplied by 1.2,namely, the relationship of “Trav<1.2 Trrf is not established, theroutine goes to a step S106 at which rust detection section 36determines a magnitude of steering torque average value Trav withrespect to specified steering torque value Trrf multiplied by 2.5.

If average value Trav of the steering torque is smaller than specifiedsteering torque value Trrf multiplied by 2.5, namely, if a relationshipof “Trav<2.5 Trrf” is established, rust detection section 36 determinesthat the abnormality is present but a degree of the abnormality is lightand performs an alarm display output which is an illumination command ofthe warning lamp for alarm command section 37. Then, the flow of FIG. 5is ended. On the other hand, if steering torque average value Trav isequal to or larger than specified steering torque value Trrf multipliedby 2.5, namely, if the relationship of “Trav<2.5 Trrf” is notestablished, rust detection section 36 determines that the degree of theabnormality is heavy, performs a system interrupting process for powersupply interrupting section 38 which is a power supply interruptioncommand for electrically driven motor 19 (a step S107), then, performsthe alarm display output (a step S108), and inputs “1” to abnormalitysettlement flag Flerr (a step S109). Then, the control flow of FIG. 5 isended.

FIG. 6 shows a flowchart representing a detail of the averaging processshown in FIG. 5.

That is to say, in the averaging process, rust detection section 36reads steering torque Tr (a step S201) and adds a sum (Tr(2)+Tr(3) . . .Tr(n−1)) of the steering torques previously processed and stocked in thenon-volatile memory to steering torque Tr(1) read at step S201 anddivide this addition value by a subtraction value (A−1) of 1 from apreviously stored predetermined value A to calculate steering torqueaverage value Trav (a step 202). Thereafter, rust detection section 36counts up a past data stock counter value Cnts representing a number ofstocks of steering torque Tr (a step S203).

Then, rust detection section 36 determines a magnitude between past datastock counter value Cnts and predetermined value A (corresponds to apredetermined interval of time according to the present invention) (astep S204). If the value of past data stock counter value Cnts is equalto or smaller than predetermined value A, namely, a number of times theprocess of step S203 is carried out does not exceed predetermined valueA (corresponds to the predetermined interval of time in the presentinvention) so that a relationship of “Cnts>predetermined value A” is notestablished, past data stock counter value Cnts count up at step S203 isinputted as n number of times (a step S205). Then, steering torque Tr(1)read at step S201 is stocked to be slid to previous value Tr(2) (a stepS206). Thereafter, the control flow of FIG. 6 is ended.

It should, herein, be noted that, if, at step S204, past data stockcounter value Cnts is larger than predetermined value A, namely, theprocess of step S203 is repeated so that past data stock counter valueCnts exceeds predetermined value A and the relationship of“Cnts>predetermined value A” is established, past data stock countervalue Cnts is cleared (a step S207) and the control flow of FIG. 6 isended.

Since, in the power steering apparatus which is structured as describedabove, a state in which steering torque average value Trav introduced bythe existing structure is larger than specified steering torque valueTrrf is defined as the abnormality and the abnormality detection iscarried out. Thus, it becomes possible to detect a progress degree ofthe rust developed on rack bar 8 and ball-screw mechanism 27 on a basisof the steering load of the apparatus. Thus, without use of anothermember, a required abnormality only can be detected.

That is to say, even if the rust is developed on rack bar 8 andball-screw mechanism 27, a serious defect (inconvenience) such as astick (or a fixation) of rack bar 8 and ball-screw mechanism 27 is notimmediately developed. The steering load is increased due to the degreeof progress of rust and, as a final stage, the serious defect such asthe stick is developed.

Therefore, since the steering load which is increased due to the degreeof progress of rust is detected, only a really dangerous abnormality inthe apparatus can be detected.

Furthermore, in the power steering apparatus, when the abnormality isdetected, the system interrupting process described above is carriedout. Hence, due to a steering feeling of steering wheel 1, thedevelopment of the abnormality can accurately be transmitted to thedriver. In this way, by promoting a necessity of maintenance such as areplacement of a component, the serious inconvenience due to theprogress of rust can be avoided before anything happens.

In addition, in a case where, during the process of the abnormalitydetection, the detected abnormality is light, the alarm display outputis performed out as a pre-stage of the system interrupting process.Thus, an attention is paid before the abnormality is developed toserious inconvenience and the necessity of maintenance can be promoted.Consequently, the driver can cope with the abnormality of the apparatusbefore the steering load is increased on a basis of the systeminterrupting process.

Furthermore, in the detection of the abnormality, the detection of theabnormality is based on the average value (steering torque average valueTrav) of a plurality of steering torques Tr in the number of times tosome degree (the predetermined interval of time) not an instantaneoussteering torque Tr. For example, in such a state in which steerablewheels 2, 3 run on a shoulder of a road or in such a state in whichsteering wheel 1 is hit (bumped) against an object, an erroneousdetermination that steering torque Tr is instantaneously increased notcaused by the development of rust as the detection of the abnormalitycan be suppressed.

In addition, when the determination dividing the predetermined number oftimes (predetermined interval of time) is made, past data stock countervalue Cnts is count up along with the calculation of steering torqueaverage value Trav and, when the counter value becomes larger thanpredetermined value A, past data stock counter value Cnts is cleared, astorage of the abnormality determination due to the increase in theinstantaneous steering torque Tr not caused by the development of rustcan be prevented and a more appropriate abnormality detection can becarried out.

FIG. 7 shows a flowchart representing a first modification of the powersteering apparatus according to the present invention and representingthe control content of FIG. 5 with the steering angle and the steeringspeed taken into consideration.

That is to say, rust detection section 36 in this flow determineswhether “1” is inputted to Flerr which is the abnormality settlementflag (a step S301). If Flerr is “1”, the flow is ended. On the otherhand, if Flerr is “0”, the routine goes to a step S302 in which steeringangle Θ ang from steering angle sensor 17 is read. Thereafter, asteering angular speed ω is calculated by time differentiating thissteering angle θ ang or steering angular speed ω is read from a sensornot shown (step S303). Then, a predetermined determination is made at astep S304.

At step S304, rust detection section 36 determines whether an absolutevalue of steering angle θ ang is smaller than a previously storedpredetermined value B or determines whether an absolute value ofsteering speed ω is smaller than a previously stored predetermined valueD, namely a relationship of “|θ ang<predetermined value B” or“|ω|<predetermined value D” is established. If the relationship isestablished, the flow is ended.

On the other hand, in a case where the above-described relationship isnot established, namely, for example, in a case where steering wheel 1is revolved to some degree and steering speed ω is developed to somedegree, namely, the relationship of “|θang|<predetermined value B or“|ω|<predetermined value D” is not established, rust detection section36 reads steering torque Tr (a step S305) and carries out the averagingprocess for the absolute value of steering torque Tr read at step S305to calculate steering torque average value Trav (a step S306).Thereafter, specified steering torque value Trrf is read (a step S307).

Thereafter, rust detection section 36 determines the magnitude betweensteering torque average value Trav calculated at step S306 and the valueof 1.2 times specified steering torque value Trrf read at step S307 (astep S308). If steering torque average value Trav is smaller than thevalue of 1.2 times specified steering torque value Trrf, namely, if therelationship of “Trav<1.2 Trrf” is established, rust detection section36 determines that the abnormality is not present and the flow of FIG. 7is ended. On the other hand, if steering torque average value Trav isequal to or larger than the value of specified steering torque valueTrrf multiplied by 1.2, namely, in a case where the relationship of“Trav<1.2 Trrf” is not established, rust detection section 36 determinesthat the abnormality is present and carries out the predetermineddetermination at a step S309 as will be described later.

At step S309, rust detection section 36 determines the magnitude betweensteering torque average value Trav and the value of 2.5 times specifiedsteering torque value Trrf. Then, if steering torque average value Travis smaller than the value of 2.5 times specified steering torque valueTrrf, namely, in a case where the relationship of “Trav<2.5 Trrf” isestablished, rust detection section 36 determines that the abnormalityis present but the degree of the abnormality is light and performs theoutput of the alarm display (a step S313). Then, the flow of FIG. 7 isended.

On the other hand, steering torque average value Trav is equal to orlarger than specified steering torque value Trrf multiplied by 2.5,namely, if the relationship of “Trav<2.5 Trrf” is not established, thedegree of the abnormality is determined to be heavy. Then, rustdetection section 36 carries out the system interrupting process (a stepS310), carries out the alarm display output (a step S311), and finallyinputs “1” to abnormality settlement flag Flerr (a step S312). Then, theflow is ended.

According to the first modification thus structured, the structures ofsteps S302, S303, and S304 are added to the control flow of FIG. 5 andthe other structures are the same. Thus, the same action and effect asFIG. 5 are obtained. Especially, in this modification, in a case wherethe relationship of “|θ ang|<predetermined value B” or“|ω|<predetermined value D” is established, the control process isended. Therefore, a traveling state of the vehicle such that thesteering torque is almost not generated, for example, the vehicletravels in a straight traveling state or the vehicle travels in aconstant steering angular state is excluded from a determination objectof the abnormality detection. In other words, a state in which steeringwheel 1 is revolved to some degree and steering speed ω is generated tosome degree can be the object of the abnormality detectiondetermination. Hence, only the state in which the steering abnormalitydue to the development of rust can be perceived can be included in thedetermination object of the abnormality detection and, thus, anabnormality detection accuracy can be improved.

FIG. 8 shows a flowchart representing a second modification of the powersteering apparatus according to the present invention and representingthe control content of FIG. 7 with a hit (bump) determination added.

That is to say, rust detection section 36 in this flow determineswhether “1” is inputted to abnormality settlement flag Flerr (a stepS401). If Flerr is “1”, the flow is ended. On the other hand, if Flerris “0”, steering angle θ ang is read (a step S402). Then, steering speedω is calculated by differentiating this steering angle θ ang withrespect to time or read steering speed w via the sensor not shown (astep S403). Thereafter, the predetermined determination is carried outat step S404 as will be described later.

At step S404, rust detection section 36 determines whether the absolutevalue of steering angle θ ang is smaller than previously storedpredetermined value B or the absolute value of steering speed ω issmaller than previously stored predetermined value D. That is to say,for example, the vehicular straight traveling state or the vehicularsteering maintaining state is determined whether the relationship of “|θang|<predetermined value” or “|ω|<predetermined value D” is established(a step S404). If the above-described relationship is established (Yes),the flow is ended.

On the other hand, if the above-described relationship is notestablished, namely, if the relationship of “|θ ang|<predetermined valueB or |ω|<predetermined value D” is not established, rust detectionsection 36 determines the magnitude between the absolute value ofsteering angle θ ang and a predetermined value R (a step S405).

At step S405, if the absolute value of steering angle θ ang is largerthan absolute value R indicating a vicinity of the hit (bump) ofsteering wheel 1, namely, the relationship of “|θ ang|>predeterminedvalue R” is established, the flow is ended. On the other hand, if theabsolute value of steering angle θ ang is equal to or smaller thanpredetermined value R, namely, the relationship of “|θang|>predetermined value R” is not established, rust detection section36 reads steering torque Tr (a step S406). Then, rust detection section36 carries out the averaging process described above for the absolutevalue of steering torque read at step S406 to calculate steering torqueaverage value Trav (a step S407) and reads specified steering torquevalue Trrf (a step S408).

Thereafter, rust detection section 36 determines the magnitude betweensteering torque average value Trav calculated by step S407 and specifiedsteering torque value Trrf read at step S408 and multiplied by 1.2 (astep S409). If steering torque average value Trav is smaller than 1.2times specified steering torque value Trrf, namely, the relationship of“Trav<1.2 Trrf” is established, rust detection section 36 determinesthat no abnormality is present and the flow is ended. On the other hand,if steering torque average value Trav is equal to or larger thanspecified steering torque value Trrf multiplied by 1.2, namely, in acase where the relationship of “Trav<1.2 Trrf” is not established, rustdetection section 36 determines that the abnormality is present andperforms a predetermined determination at a step S410.

At step S410, rust detection section 36 determines the magnitude betweensteering torque average value Trav and 2.5 times specified steeringtorque value Trrf (a step S410). Then, if steering torque average valueTrav is smaller than 2.5 times specified steering torque Trrf, namely,steering torque average value Trav is smaller than 2.5 times specifiedsteering value Trrf, namely, in a case where the relationship of“Trav<2.5 Trrf” is established, rust detection section 36 determinesthat the abnormality is present but the degree of the abnormality islight, performs the alarm display output (a step S414), and, thereafter,the flow is ended.

On the other hand, in a case where steering torque average value Trav isequal to or larger than 2.5 times specified steering torque value Trrf,namely, if the relationship of “Trav<2.5 Trrf” is not established, rustdetection section 36 performs the system interrupting process (a stepS411), performs the alarm display output (a step S412), and, finally,“1” is inputted to abnormality settlement flag Flerr (a step S413).Then, the flow is ended.

According to the second modification described above, step S405 is addedto the first modification. The other structures are the same as those ofthe first modification. The same actions and advantages as the firstmodification are obtained. Especially, at the determination of stepS405, in a case where the relationship of “|θ ang|>predetermined valueR” is established, the flow is ended.

Therefore, if predetermined value R is, for example, set to a positionin the vicinity to the hit (bump) of steering wheel 1. A case where thesteering torque is increased due to the hit (bump) of the steering wheeland not due to the development of rust can be excluded from theabnormality determination. Therefore, a further improvement of theabnormality detection accuracy can be achieved.

FIG. 9 shows a flowchart representing a third modification of the powersteering apparatus according to the present invention and representingthe control content of FIG. 5 with the steering angle and yaw taken intoconsideration.

That is to say, rust detection section 36 in this flow determineswhether “1” is inputted to abnormality settlement flag Flerr (a stepS501). If Herr indicates “1”, the flow is ended. On the other hand, ifFlerr is “0”, steering angle θ ang is read (a step S502) and yaw Yw isread from yaw rate sensor 41 (a step S503).

Then, if the absolute value of steering angle θ ang is smaller than apreviously stored predetermined value B or the absolute value of yaw Ywis smaller than a previously stored predetermined value J, namely, thevehicle traveling state corresponds to, for example, a straighttraveling state of the vehicle, a drift state in which tires are notgripped so that rust detection section 36 determines whether arelationship of “|θang|<predetermined angle B or |Yw|<predeterminedvalue J” is established (a step S504). If the above-describedrelationship is established, rust detection section 36 determines thatno abnormality is present and the flow is ended. On the other hand, in acase where the above-described relationship is not established, rustdetection section 36 reads steering torque Tr (a step S505), calculatessteering torque average value Trav by performing the average process forthe absolute value of read steering torque Tr (a step S506) and,thereafter, reads specified steering torque value Trrf (a step S507).

Then, rust detection section 36 determines the magnitude betweensteering torque average value Trav calculated at step S506 and 1.2 timesspecified steering torque value Trrf read at step S507 (a step S508). Ifsteering torque average value Trav is smaller than 1.2 times specifiedsteering torque value Trrf, namely, in a case where the relationship of“Trav<1.2 Trrf” is established, rust detection section 36 determinesthat no abnormality is present and the flow is ended.

On the other hand, in a case where steering torque average value Trav isequal to or larger than 1.2 times specified steering torque value Trrf,namely, the relationship of “Trav<1.2 Trrf” is not established, rustdetection section 36 determines the magnitude between steering torqueaverage value Trav and specified steering torque value Trrf multipliedby 2.5 (a step S509).

Furthermore, in a case where steering torque average value Trav issmaller than 2.5 times specified steering torque value Trrf, namely, ina case where the relationship of “Trav<2.5 Trrf” is established, rustdetection section 36 determines that the abnormality is present but thedegree of abnormality is light and performs the alarm display output (astep S513). Then, the flow is ended. On the other hand, in a case wheresteering torque average value Trav is equal to or larger than 2.5 timesspecified steering torque value Trrf, namely, in a case where therelationship of “Trav<2.5 Trrf” is not established, rust detectionsection 36 determines that the degree of abnormality is heavy, performsthe alarm display output (a step S511), and finally inputs “1” toabnormality settlement flag Flerr (a step S512). Then, the flow isended.

According to the third modification, steps S502 through S504 are addedto the first preferred embodiment. The other structures are the same asthe first preferred embodiment. Thus, the same action and effect as thefirst preferred embodiment are obtained. Especially, in thismodification, rust detection section 36 determines whether therelationship of “|θ ang|<predetermined value B” or “|Yw|<predeterminedvalue J” is established and, if this relationship is established, theprocess is ended. Hence, a state in which the vehicle is traveled is astraight travel and an increase in the steering torque in a specialtraveling state such as a drift state in which the tires are not grippedcan be excluded from the object of the abnormality determination. Thefurther improvement of the abnormality determination accuracy can beachieved.

FIG. 10 shows a flowchart representing a fourth modification the powersteering apparatus according to the present invention and representingthe control content of FIG. 5 with the road wheel speeds taken intoconsideration.

That is to say, rust detection section 36 determines whether “1” isinputted to abnormality settlement flag Flerr (step S601). If Flerr is“1”, the flow is ended. On the other hand, if Flerr is “0”, rustdetection section 36 reads right road wheel speed Vwr from right roadwheel speed sensor 42 and reads left road wheel speed Vwl from left roadwheel speed sensor 43 (a step S602) and subtracts left road wheel speedVwl from right road wheel speed Vwr to calculate a front road wheelspeed left and right difference Vw θ (a step S603).

Then, rust detection section 36 determines whether an absolute value offront road wheel speed left and right difference Vw θ is smaller than apreviously stored predetermined value K, namely, whether a relationshipof “|Vw θ|<predetermined value K” is established (a step S604). If thisrelationship is established, rust detection section 36 determines thatno abnormality is present and the flow is ended.

On the other hand, if the above-described relationship is notestablished, rust detection section 36 reads steering torque Tr (a stepS605), performs the averaging process for the absolute value of steeringtorque Tr to calculate steering torque average value Trav (a step S606),and, thereafter, reads specified steering torque value Trrf (a stepS607).

Then, rust detection section 36 determines the magnitude betweensteering torque average value Trav calculated at step S606 and 1.2 timesspecified steering torque value Trrf (a step S608). Then, if steeringtorque average value Trav is smaller than 1.2 times specified issteering torque value Trrf, namely, if the relationship of “Trav<1.2Trrf” is established, rust detection section 36 determines that theabnormality is not present and the flow is ended. On the other hand, ifsteering torque average value Trav is equal to or larger than the valueof 1.2 times specified steering torque value Trrf, namely, if therelationship of “Trav<1.2 Trrf” is not established, rust detectionsection 36 determines the magnitude between steering torque averagevalue Trav and 2.5 times specified steering torque value Trrf (a stepS609).

At step S609, if steering torque average value Trav is smaller than 2.5times specified steering torque value Trrf, namely, if the relationshipof “Trav<2.5 Trrf” is established, rust detection section 36 determinesthat, although the abnormality is present, the degree of the abnormalityis light. Then, after rust detection section 36 performs the alarmdisplay output (a step S613), the flow is ended. On the other hand, in acase where steering torque average value Trav is equal to or larger than2.5 times specified steering torque value Trrf, namely, if therelationship of “Trav<2.5 Trrf” is not established, rust detectionsection 36 determines that the degree of the abnormality is heavy,performs the system interrupting process (a step S610), performs thealarm display output (a step S611), and, finally, “1” is inputted toabnormality settlement flag Flerr (a step S612), and this flow is ended.

According to the fourth modification structured as described above,steps S602 through S604 are added to the first preferred embodiment.Since the other structure are the same as the first embodiment. Thus,the same action and effect as the first embodiment can be obtained.Especially, in this modification, in place of read of steering angle θang, front road wheel speed left and right difference Vw θ from left andright road wheel speeds Vwr, Vwl is calculated and if the relationshipof “Vw θ<predetermined value K” is established, the process is ended.Thus, the traveling state corresponds to the straight traveling statecan be excluded from the object of the abnormality determination. Itshould be noted that by a combination of the steering angular speed asthe first modification, the so-called maintaining state of the constantsteering angle may be excluded from the object of the abnormalitydetermination. In addition, the combination of the yaw Yw as the thirdmodification, the drift state may be eliminated from the object of theabnormality determination.

FIG. 11 shows a flowchart representing a fifth modification of the powersteering apparatus according to the present invention and representingthe control content of FIG. 5 with the average value immediately beforean ignition switch is, at a previous time, turned off taken intoconsideration.

That is to say, rust detection section 36 determines whether it is firsttime passed when an ignition switch is turned on (a step S701). In acase where it is not first time passed, namely, in a case where once ormore of the process of the flow in FIG. 11 has been carried out sincethe ignition switch has been turned on, rust detection section 36determines whether “1” is inputted to abnormality settlement flag Flerr(a step S702). If “1” is inputted to abnormality settlement flag Flerr,the routine goes to a step S712 as will be described later.

On the other hand, in a case where it is first time passed at step S701,namely, the process of the flow of FIG. 11 is not carried out any moresince the ignition switch is turned on, rust detection section 36 readssteering torque average value Trav immediately before the previousignition switch is turned off and stored in a memory at a step S716(which will be described below) (a step S713) and sets an immediateprevious time value Tr(n) as will be described later with this as aninitial value (a step S714) and, thereafter, the routine goes to stepS702.

In a case where Flerr is determined to be “0” at step S702, rustdetection section 36 reads steering torque Tr (a step S703), carries outthe averaging process for the absolute value of read steering torque Trto calculate steering torque average value Trav (a step S704), and,thereafter, reads specified steering torque value Trrf (a step S705).

Then, rust detection section 36 determines the magnitude betweensteering torque average value Trav calculated at step S704 and the valueof 1.2 times specified steering torque value Trrf read at step S705 (astep S706). If steering torque average value Trav is smaller than 1.2times specified steering torque value Trrf, namely, if the relationshipof “Trav<1.2 Trrf” is established, the routine goes to a step S712 aswill be described later.

On the other hand, in a case where steering torque average value Trav isequal to or larger than 1.2 times specified steering torque value Trrf,namely, if the relationship of “Trav<1.2 Trrf” is not established, rustdetection section 36 determines that the abnormality is present and,thereafter, determines the magnitude between steering torque averagevalue Trav and determines the magnitude between steering torque averagevalue Trav and the value of 2.5 times specified steering torque valueTrrf (a step S707).

Then, in a case where steering torque average value Trav is determinedto be smaller than 2.5 times specified steering torque value Trrf,namely, in a case where the relationship of “Trav<2.5 Trrf” isestablished, the abnormality is present but the degree of theabnormality is light. Then, rust detection section 36 performs the alarmdisplay output (a step S711) and the routine goes to a step S712 as willbe described later.

On the other hand, in a case where, at step S707, steering torqueaverage value Trav is equal to or larger than the value of 2.5 timesspecified steering torque value Trrf, namely, if the relationship of“Trav<2.5 Trrf” is not established, rust detection section 36 determinesthat the degree of the abnormality is heavy, subsequently, performs thesystem interrupting process (a step S708), and, thereafter, the alarmdisplay output is performed (a step S709), “1” is inputted toabnormality settlement flag Flerr (a step S710). Thereafter, at stepS712, rust detection section 36 determines whether ignition switch IGNis turned off (a step S712).

Then, if ignition switch IGN is turned off (Yes) at step S712, rustdetection section 36 starts a self-holding of a power supply of amicrocomputer (a step S715) and stores steering torque average valueTrav into the non-volatile memory (a step S716) and, finally, a powersupply of the microcomputer is turned off (a step S717). Then, thepresent flow is ended.

On the other hand, in a case where rust detection section 36 determinesthat ignition switch IGN is not turned off at step S712, the flow isimmediately ended.

FIG. 12 shows a flowchart representing details of the averaging processshown in FIG. 11.

That is to say, rust detection section 36 in this flow determineswhether the present routine is first time passage at a time of theignition switch turned on (a step S801). If rust detection section 36determines that this is not first time passed, rust detection section 36reads steering torque Tr (a step S802).

On the other hand, in a case of the first time passage (Yes at stepS801), rust detection section 36 reads steering torque average valueTrav immediately before the previous ignition off stored in thenon-volatile memory (a step S808) and sets to an immediate previousvalue Tr(n) with this as the initial value (a step S809). Thereafter,the routine goes to step S802.

A sum of steering torque average value Trav (in a case of the first timepassage) immediately before the previous ignition switch turn off readat step S808 or steering torque average value Trav calculated at theprocess at the previous passage time with the steering torque after theignition switch turned on (Tr(1)+Tr(2)+Tr(3)+ . . . Tr(n−1)) is dividedby the previously stored predetermined value A to calculate steeringtorque average value Trav (a step S803). Thereafter, past data stockcounter value Cnts indicating the stock number of steering torque Tr iscounted up (a step S804).

Then, rust detection section 36 determines the magnitude between pastdata stock counter value Cnts obtained at above-described step S803 andpredetermined value A (a step S805). If past stock counter value Cnts islarger than predetermined value A (Yes), namely, the process at stepS804 is repeated and past data stock counter value Cnts exceedspredetermined value so that the relationship of “Cnts>predeterminedvalue” is established. In this case, after past data stock counter valueCnts is cleared (a step S810), the flow is ended.

On the other hand, in a case where past data stock counter value Cnts isequal to or smaller than predetermined value A, namely, in a case wherethe number of times the process at step S804 is carried out is not inexcess of predetermined value A (predetermined interval of time) so thatthe relationship of “Cnts>predetermined value A” is not established,past data stock counter value Cnts count up at step S804 is inputted asn-th number of times (a step S806), steering torque Tr read at step S802is stocked to a previous value Tr(2) (a step S807), and, thereafter, theflow is ended.

According to the fifth modification structured as described above, thestructures of steps S712 through S717 are added to the first preferredembodiment. The other structures are the same as the first preferredembodiment. Thus, the same action and effects as the first preferredembodiment can be obtained. Especially, in the fifth modification, sincesteering torque average value Trav immediately before the power supplyof the microcomputer is turned off by the turning off of the ignitionswitch is stored in the non-volatile memory, the information of steeringtorque average value Trav before the ignition switch is turned off atthe subsequent ignition switch being turned on can be utilized. Forexample, in a case where the vehicle is left unused for a constantinterval of time so that the rust is progressed, the detection of theabnormality due to the rust can be made at an early stage. Hence, afurther improvement of the abnormality detection accuracy can beachieved.

FIG. 13 shows a flowchart representing a sixth modification of the powersteering apparatus according to the present invention and representingan addition of a weighting to the averaging process at step S803 of FIG.12.

That is to say, rust detection section 36 in this flow determineswhether this corresponds to the first time passage case at a time of theignition switch being turned on (a step S901). If rust detection section36 determines that it is not first time passed, rust detection section36 reads steering torque Tr (a step S902).

On the other hand, in a case where this corresponds to the first timepassage (Yes at step S901), rust detection section 36 reads steeringtorque average value Trav immediately before the previous ignition(switch) off stored in the non-volatile memory (a step S908). Then, withthis read value as an initial value, rust detection section 36 setsinitial value to the immediate prior value Tr(n) of steering torque (astep S909) and the routine goes to a step S902.

Then, a sum of a value of a weight coefficient K1 multiplied by steeringtorque average value Trav (in a case of the first time passage)immediately before the previous ignition (switch) turned off read atstep S908 or steering torque average value Trav calculated at theprocess in the first time passage and a value of another weightcoefficient K2 multiplied by a sum of the steering torque after theignition switch is turned on (Tr(1)+Tr(2) Tr(3) . . . Tr(n−1)) isdivided by a value of the sum of weight coefficients K1+K2 multiplied bythe previously stored predetermined value A to calculate steering torqueaverage value Trav (a step S903). Thereafter, past data stock countervalue Cnts representing the number of stocks of steering torque Tr iscounted up (a step S904).

Next, rust detection section 36 determines the magnitude between pastdata stock counter value Cnts obtained at step S904 and predeterminedvalue A (a step S905). If past data stock counter value Cnts is largerthan predetermined value A, namely, in a case where the process of stepS904 is repeated for the predetermined interval of time, past data stockcounter value Cnts is in excess of predetermined value, and therelationship of “Cnts>predetermined value A” is established, past datastock counter value Cnts is cleared (a step S910) and, then, the flow isended.

On the other hand, in a case where past data stock counter value Cnts isequal to or smaller than predetermined value A, namely, in a case wherethe number of times the process of step S904 is carried out is not inexcess of predetermined value A (predetermined interval of time), andthe relationship of “Cnts>predetermined value A” is not established,past data stock counter value Cnts counted up at step S904 is inputtedas n-th number of times (a step S906), steering torque Tr read at stepS902 is stocked to previous value Tr(2) (a step S907), and, then, theflow is ended.

According to the sixth modification structured as described above, theweighting is carried out for steering torque average values Travimmediately before the previous ignition (switch turned) off and afterthe ignition (switch turned) off so that steering torque average valueTrav immediately before the previous ignition (switch turned) offsampled for a long term can effectively be utilized. Thus, a moreaccurate steering torque average value Trav can be calculated.

FIG. 14 shows a flowchart representing a seventh modification of thepower steering apparatus according to the present invention andrepresenting the control content of FIG. 5 to which a process ofgradually reducing motor command current TRr is added.

That is to say, rust detection section 36 in this flow determineswhether “1” is inputted to abnormality settlement flag Flerr (a stepS1001). If Flerr is “1”, the flow is ended. On the other hand, if Flerris “0”, rust detection section 36 reads steering torque Tr (a stepS1002) and carries out the averaging process as described with referenceto FIG. 6 for the absolute value of read steering torque Tr to calculatesteering torque average value Trav (a step S1003) and, thereafter, readsspecified steering torque value Trrf (a step S1004).

Then, rust detection section 36 determines the magnitude betweensteering torque average value Trav calculated at step S1003 and 1.2times specified steering torque value Trrf read at step S1004 (a stepS1005). In a case where steering torque average value Trav is equal toor larger than 1.2 times specified steering torque value Trrf, namely,in a case where the relationship of “Trav<1.2 Trrf” is not established,rust detection section 36 determines that the abnormality is presentand, thereafter, determines the magnitude between steering torqueaverage value Trav and 2.5 times specified steering torque value Trrf (astep S1006).

In a case where steering torque average value Trav is equal to or largerthan 2.5 times specified steering torque value Trrf, namely, in a casewhere the relationship of “Trav<2.5 Trrf is not established, rustdetection section 36 determines that the degree of the abnormality isheavy, performs the system interrupting process (a step S1007), andperforms the alarm display output (a step S1008). Then, finally, rustdetection section 36 inputs “1” to abnormality settlement flag Flerr (astep S1009) and the flow is ended.

On the other hand, at step S1006, in a case where rust detection section36 determines that steering torque average value Trav is smaller than2.5 times specified steering torque value Trrf, namely, in a case wherethe relationship of “Trav<2.5 Trrf” is established, rust detectionsection 36 determines that the abnormality is present but the degree ofthe abnormality is light, performs the alarm display output (a stepS1010), and performs a gradual decrease process of motor command currentTRr (a step S1011). Then, the flow is ended.

In addition, at step S1005, in a case where rust detection section 36determines that steering torque average value Trav is smaller than 1.2times specified steering torque value Trrf, namely, in a case where therelationship of “Trav<1.2 Trrf” is established, rust detection section36 determines that the abnormality is not present or the abnormality iseliminated and performs a gradual increase process of motor commandcurrent TRr (a step S1012). Then, the flow is ended.

According to the seventh modification as described above, the structuresof steps S1011 and S1012 are added to the first preferred embodiment.The other structures are the same as the first preferred embodiment.Thus, the same action and effect as the first preferred embodiment canbe achieved. Especially, in this modification, when rust detectionsection 36 determines that the abnormality is present but the degree ofthe abnormality is light, motor command current TRr is gradually deceaseprocessed. Thus, the abnormality can be informed to the driver withoutgiving an abrupt load to the driver as in a case of the systeminterrupting process.

In addition, in this modification, motor command current TRr isgradually decrease processed in accordance with steering torque averagevalue Trav. Thus, as compared with, for example, a case where motorcommand current TRr is gradually decrease processed in accordance withtime, an abrupt increase of the steering load to the driver before andafter the straight traveling state can be prevented. It should be notedthat, in place of the gradual decrease process of motor command currentTRr, an upper limit value of the motor torque may gradually be decreaseprocessed from a specified upper limit value.

As described above, in the first preferred embodiment and respectivemodifications related to the first preferred embodiment, steering torqueaverage value Trav is calculated and the abnormality is detected bycomparing steering torque average value Trav and specified steeringtorque value Trrf. However, parameters of the abnormality determinationmay appropriately freely be set in accordance with specifications of theapparatus. In addition, in place of steering torque Tr, motor commandcurrent TRr or motor actual current Ir may be used. In this case, inplace of steering torque average value Trav, the average value of motorcommand current TRr or motor actual current Ir is used.

Second Embodiment

FIG. 15 shows a control block diagram representing details related to asecond preferred embodiment from among the control structure of controlunit (ECU) 18 shown in FIG. 1.

In this control unit 18, rust detection section 50 is constituted onlyby abnormality detection circuit 51. In this abnormality detectioncircuit 51, motor command current TRr and motor actual current Ir areinputted to the abnormality detection circuit 51. This point isdifferent from the first preferred embodiment. When these values (thesteering load corresponding value) are compared with specified value anda frequency that the steering load corresponding value exceeds thespecified value is larger than the predetermined value, the abnormalityof the apparatus is detected. In addition, abnormality detection circuit51 outputs a torque control signal Ts which limits a torque upper limitvalue of electrically driven motor 19 under a predetermined condition tomotor control section 33.

Hereinafter, the control content of rust detection section 50 willspecifically be explained on a basis of FIGS. 16 through 21.

FIG. 16 shows a flowchart representing a process content of determiningthe abnormality by calculating a frequency of abnormality in place ofthe averaging process of the control content of FIG. 5.

That is to say, rust detection section 50 in this flow determineswhether “1” is inputted to abnormality settlement flag Flerr (a stepS1101). If Flerr is “1”, the flow is ended. On the other hand, if Flerris “0”, rust detection section 50 reads steering torque Tr (a stepS1102). Then, rust detection section 50 reads an abnormality steeringtorque value Terr previously stored as the specified value whichprovides a criterion of the abnormality determination (a step S1103).Thereafter, rust detection section 50 counts up a timer counter valueTnts which serves as a confirmation of the abnormality frequency duringa predetermined sampling number of times (corresponds to a predeterminedinterval of time in the present invention) (“1” is added to the timercounter value Tnts) (a step S1104).

Next, rust detection section 50 determines the magnitude between timercounter value Tnts obtained at step S1104 and a previously storedpredetermined value E (a step S1105). In a case where timer countervalue Tnts is smaller than predetermined value E, namely, in a casewhere the relationship of “Tnts<predetermined value E” is established,rust detection section 50 determines the magnitude between steeringtorque Tr read at step S1102 and a previously stored abnormalitysteering torque value Terr (a step S1106).

It should be noted that, in a case where steering torque Tr is equal toor larger than abnormality steering torque value Terr, namely, in a casewhere the relationship of “Tr<Terr” is not established, rust detectionsection 50 counts up an abnormality counter value Cerr (“1” is added toabnormality counter value Cerr) (a step S1111). Next, rust detectionsection 50 determines the magnitude between abnormality counter valueCerr and a previously stored predetermined value H (a step S1107). Onthe other hand, in a case where, at step S1106, steering torque Tr issmaller than an abnormality steering torque value Terr, namely, in acase where the relationship of “Tr<Terr” is established, rust detectionsection 50 determines that the abnormality is not present and theroutine goes to step S1107.

In addition, at step S1105, in a case where timer counter value Tnts isequal to or larger than predetermined value E, namely, in a case wherepredetermined sampling number of times E has been reached and therelationship of “Tnts<predetermined value E” is not established,abnormality counter value Cerr is cleared (a step S1112) and timercounter value Tnts is cleared (a step S1113). Then, the flow is ended.

Then, at step S1107, in a case where abnormality counter value Cerr isequal to or smaller than predetermined value H, namely, in a case wherethe relationship of “Cerr>predetermined value H” is not established,rust detection section 50 determines that no abnormality is present andthe flow is ended. On the other hand, in a case where abnormalitycounter value Cerr is larger than a predetermined value H, namely, in acase where the relationship of “Cerr>predetermined value H” isestablished, rust detection section 50 determines that the abnormalityis present. Then, rust detection section 50 inputs “1” to abnormalitysettlement flag Flerr (a step S1108), performs the system interruptingprocess (a step S1109), and performs the alarm display output (a stepS1110). Then, the flow is ended.

According to the second preferred embodiment described above, when thefrequency that steering torque Tr as the steering load correspondingvalue exceeds abnormality steering torque value Terr as the specifiedvalue is larger than predetermined value H, the abnormality is detected.In the same way as the first preferred embodiment, no another member isnot needed and only the abnormality can be detected.

In addition, in the second preferred embodiment, the presence or absenceof abnormality of the apparatus is determined according to theabnormality frequency in place of steering torque average value Trav.Therefore, even in a case where such a situation that the steeringtorque Tr is instantaneously enlarged not due to the development of therust but due to a driving state such that steering wheel 1 is hit(bumped) against a wall or tires run over a curb stone, an influence ofgiving the abnormality determination is small as compared with the firstpreferred embodiment and a more highly accurate abnormality detectioncan be achieved.

Furthermore, when timer counter value Tnts has reached to thepredetermined sampling number of times (predetermined value E),abnormality counter value Cerr is cleared and, thereafter, timer countervalue Tnts is cleared. An influence of a cumulative increase of steeringtorque Tr generated due to the driving state not caused by thedevelopment of rust is furthermore reduced.

FIG. 17 shows a flowchart representing a first modification of thesecond preferred embodiment and representing an addition of the processin accordance with the number of the abnormality frequency to thecontrol of FIG. 16.

That is to say, rust detection section 50 determines whether “1” isinputted to abnormality settlement flag Flerr (a step S1201). If Flerris “1”, the flow is ended. On the other hand, if Flerr is “0”, rustdetection section 50 reads steering torque Tr (a step S1202). Then, rustdetection section 50 reads abnormality steering torque value Terr (astep S1203) and, thereafter, counts up timer counter value Tnts (“1” isadded to timer counter value Tnts) (a step S1204).

Then, rust detection section 50 determines the magnitude between timercounter value Tnts obtained at step S1204 and previously storedpredetermined value E (a step S1205). In a case where timer countervalue Tnts is smaller than predetermined value E, namely, in a casewhere the relationship of “Tnts<predetermined value E” is established,rust detection section 50 determines the magnitude between steeringtorque Tr read at step S1202 and previously stored abnormality steeringtorque value Terr (a step S1206).

In a case where steering torque Tr is equal to or larger thanabnormality steering torque value Terr, namely, in a case where therelationship of “Tr<Terr” is not established, abnormality counter valueCerr is counted up (“1” is added to abnormality counter value Cerr) (astep S1211). Then, rust detection section 50 determines the magnitudebetween abnormality counter value Cerr and a previously storedpredetermined value H1 (a step S1207). On the other hand, at step S1206,in a case where steering torque Tr is smaller than abnormality steeringtorque value Terr, namely, in a case where the relationship of “Tr<Terris established, the routine goes to step S1207.

Then, at step S1207, in a case where abnormality counter value Cerr islarger than predetermined value H1, namely, in a case where therelationship of “Cerr>predetermined value H1” is established, rustdetection section 50 determines that the abnormality whose degree isheavy is present, “1” is inputted to abnormality settlement flag Flerr(a step S1208), performs the system interrupting process (a step S1209),and finally performs the alarm display output (a step S1210). Then, theflow is ended.

On the other hand, in a case where abnormality counter value Cerr isequal to or smaller than predetermined value H1, namely, in a case wherethe relationship of “Cerr>predetermined value H1” is not established,rust detection section 50 determines that at least serious abnormalitydoes not occur and determines the magnitude between abnormality countervalue Cerr and predetermined value H2 (a step S1212).

Then, in a case where abnormality counter value Cerr is larger thanpredetermined value H2, namely, in a case where the relationship of“Cerr>predetermined value H2” is established, rust detection section 50determines that the degree of abnormality is middle. Then, rustdetection section 50 performs the alarm display output (a step S1213),sets the upper limit of the motor torque to 30% of specified value (astep S1214), and the flow is ended.

On the other hand, at step S1212, in a case where abnormality countervalue Cerr is equal to or smaller than a predetermined value H3, namely,in a case where the relationship of “Cerr>predetermined value H2” is notestablished, rust detection section 50 determines that at least middledegree of abnormality does not occur and determines the magnitude ofabnormality counter value Cerr and predetermined value H3 (a stepS1215).

Then, at step S1215, in a case where abnormality counter value Cerr islarger than a predetermined value H3, namely, in a case where therelationship of “Cerr>predetermined value H3” is established, rustdetection section 50 determines that the abnormality of the light degreeis present, performs the alarm display output (a step S1216) and setsthe upper limit of the motor torque to 50% of the specified upper limitvalue (a step S1217). Then, the flow is ended.

On the other hand, at step S1215, in a case where abnormality countervalue Cerr is equal to or smaller than predetermined value H3, namely,in a case where the relationship of “Cerr>predetermined value H3” is notestablished, rust detection section 50 determines that no abnormality ispresent and the flow is ended.

In addition, at step S1205, in a case where timer counter value Tnts isequal to or larger than predetermined value E, namely, the predeterminedsampling number of times has been reached and the relationship of“Tnts<predetermined value E” is not established, abnormality countervalue Cerr is cleared (a step S1218) and timer counter value Tnts iscleared (a step S1219). Thereafter, the flow is ended.

According to the first modification described above, the steps S1215through S1217 are added to the second preferred embodiment. The otherstructures are the same as the second preferred embodiment. Thus, thesame action and effect as the second preferred embodiment can beachieved. Especially, in this modification, such a stepwise processthat, in a case where the abnormality of the light degree is determinedto occur, the upper limit value of the motor torque is set to 50% of thespecified value, in a case where the abnormality of the middle degree isdetermined to occur, the upper limit value of the motor torque is set to30% of the specified value, and in a case where the abnormality of theheavy degree is determined to occur, the system interrupting process iscarried out, is carried out. Thus, the abnormality of the apparatus canmore clearly be informed to the driver by the stepwise increase of thesteering load. A compatibility of a warning notice and a prevention ofthe abrupt increase of the steering load to the driver becomes possible.

It should be noted that, in place of the stepwise load, the gradualdecrease process of motor command current TRr as explained withreference to FIG. 14 may be carried out.

FIG. 18 shows a flowchart representing a second modification of thesecond preferred embodiment and representing a use of motor commandcurrent TRr in place of steering torque Tr in the control of FIG. 16.

That is to say, rust detection section 50 in this flow determineswhether “1” is inputted to abnormality settlement flag Flerr (a stepS1301). If Flerr is “1”, the flow is ended. On the other hand, if Flerris “0”, rust detection section 50 reads motor command current TRr froman assistance current calculating section 32 (a step S1302), reads apreviously stored abnormality range MAP1 (a step S1303), reads vehiclespeed Vs from vehicle speed sensor 29 (a step 1304), and counts up timercounter value Tnts (“1” is added to timer counter value Tnts) (a stepS1305).

Then, rust detection section 50 determines the magnitude between timercounter value Tnts obtained at step S1305 and previously storedpredetermined value E (a step S1306). If timer counter value Tnts issmaller than predetermined value E, namely, in a case where therelationship of “Tnts<predetermined value E” is established, rustdetection section 50 determines the magnitude between motor commandcurrent TRr read at step S1302 and an abnormality range value Trerrwithin abnormality range MAP1 read at step S1303 (a step S1307).

It should be noted that the details of abnormality range MAP1 will beexplained. As shown in FIG. 19, motor command current TRr with respectto vehicle speed Vs falls within an normal range of a lower side of FIG.19 with abnormality range value Trerr denoted by a curved line C1 as aboundary. An upper side of FIG. 19 is the abnormality range. It shouldbe noted that, when motor command current TRr with respect to vehiclespeed Vs falls on abnormality range value Terr, the abnormality range isincluded.

Then, at step S1307 of FIG. 18, in a case where motor command currentTRr is equal to or larger than abnormal steering torque value Trerr,namely, in a case where motor command current TRr with respect tovehicle speed Vs falls within the abnormality range of FIG. 19 so thatthe relationship of “TRr<Trerr” is not established, rust detectionsection 50 determines that the abnormality is present, counts upabnormality counter value Cerr (“1” is added to abnormality countervalue Cerr) (a step S1312), and determines the magnitude betweenabnormality counter value Cerr and previously stored value H (a stepS1308). On the other hand, at step S1307, in a case where motor commandcurrent TRr is smaller than abnormality steering torque value Trerr,namely, in a case where motor command current TRr with respect tovehicle speed Vs does not fall within abnormality range of FIG. 19 sothat the relationship of “TRr<Trerr” is established, rust detectionsection that the abnormality is not present and the routine goes to stepS1308.

In addition, at step S1306, in a case where timer counter value Tnts isequal to or larger than predetermined value E, namely, the predeterminedsampling number of times E has been reached and the relationship of“Tnts<predetermined value E” is not established, rust detection section50 clears abnormality counter value Cerr (a step S1313) and clears timercounter value Tnts (a step S1314). Then, the flow is ended.

Then, at step S1308, in a case where abnormality counter value Cerr isequal to or smaller than predetermined value H, namely, in a case wherethe relationship of “Cerr>predetermined value H” is not established,rust detection section 50 determines that the abnormality is not presentand the flow is ended. On the other hand, at step S1308, in a case whereabnormality counter value Cerr is larger than predetermined value H,namely, in a case where the relationship of “Cerr>predetermined value H”is established, rust detection section 50 determines that theabnormality is present, adds “1” to abnormality settlement flag Flerr (astep S1309), carries out the system interrupting process (a step S1310),and finally performs the alarm display output (a step S1311). Then, theflow is ended.

As described above, according to the second modification, when thefrequency that the motor command current as the steering loadcorresponding value exceeds abnormality range value Trerr as thespecified value is larger than predetermined value H, the abnormality isdetected. Therefore, in the same way as the second preferred embodiment,a separate member as the conventional technique is not needed and therequired abnormality only can be detected.

FIG. 20 shows a flowchart representing a third modification of thesecond preferred embodiment and representing the use of motor actualcurrent Ir in place of steering torque Tr in the control of FIG. 16.

That is to say, rust detection section 50 in this flow determineswhether “1” is added to abnormality settlement flag Flerr (a stepS1401). If Flerr is “1”, the flow is ended. On the other hand, if Flerris “0”, rust detection section 50 reads motor actual current Ir frommotor drive section 34 (a step S1402), reads a previously storedabnormality range MAP2 (a step S1403), and reads vehicle speed Vs fromvehicle speed sensor 29 (a step S1404). Thereafter, rust detectionsection 50 counts up timer counter value Tnts (“1” is added to timercounter value Tnts) (a step S1405).

Then, rust detection section 50 determines the magnitude between timercounter value Tnts obtained at step S1405 and previously storedpredetermined value E (a step S1406). In a case where timer countervalue Tnts is smaller than predetermined value E, namely, in a casewhere the relationship of “Tnts<predetermined value E” is established,rust detection section 50 determines the magnitude between motor actualcurrent Ir read at step S1402 and abnormality range value lerr withinabnormality range MAP2 read at step S1403 (step S1407).

It should be noted that the details of abnormality range map MAP2 willbe explained. As shown in FIG. 21, motor actual current Ir with respectto vehicle speed Vs falls within an normal range of a lower side of FIG.19 with abnormality range value lerr denoted by a curved line C2 as aboundary. An upper side of FIG. 21 is the abnormality range. It shouldbe noted that, when motor actual current Ir with respect to vehiclespeed Vs falls on abnormality range value lerr, the abnormality range isincluded.

Then, at step S1407 of FIG. 20, if motor actual current Ir is equal toor larger than abnormality range value lerr, namely, in a case wheremotor actual current Ir with respect to vehicle speed Vs falls withinthe abnormality range in FIG. 21 so that the relationship of “Ir<lerr”is not established, rust detection section 50 determines that theabnormality is present, counts up abnormality counter value Cerr (“1” isadded to abnormality counter Cerr)(a step S1412). Then, rust detectionsection 50 determines the magnitude between abnormality counter valueCerr and previously stored predetermined value H (a step S1408). On theother hand, at step S1407, in a case where motor actual current Ir issmaller than abnormality range value lerr, namely, in a case where motoractual current Ir with respect to vehicle speed Vs does not fall withinthe abnormality range in FIG. 21 so that the relationship of “Ir<lerr”is established, rust detection section 50 determines that theabnormality is not present and the routine goes to step S1408.

In addition, at step S1406, in a case where timer counter value Tnts isequal to or larger than predetermined value E, namely, predeterminedsampling number of times E has been reached and the relationship of“Tnts<predetermined value E” is not established, rust detection section50 clears abnormality counter Cerr (a step S1413) and clears timercounter value Tnts (a step S1414). Then, the flow is ended.

Then, at step S1408, in a case where abnormality counter value Cerr isequal to or smaller than predetermined value H, namely, in a case wherethe relationship of “Cerr>predetermined value H” is not established,rust detection section 50 determines that no abnormality is present andthe flow is ended.

On the other hand, in a case where abnormality counter value Cerr islarger than predetermined value H, namely, in a case where therelationship of “Cerr>predetermined value H” is established, rustdetection section 50 determines that the abnormality is present. Then,rust detection section 50 inputs “1” to abnormality settlement flagFlerr (a step S1409), performs the system interrupting process (a stepS1410), and, then, performs the alarm display output (a step S1411).Then, the flow is ended.

As described above, according to the third modification, when thefrequency that motor actual current value Ir as the steering loadcorresponding value exceeds abnormality range value lerr as thespecified value is larger than predetermined value H, the abnormality isdetected. Thus, in the same way as the second preferred embodiment, noseparate member as the conventional technique is needed and the requiredabnormality only can be detected.

It should be noted that, in the second preferred embodiment and each ofthe related modifications, the process as shown in FIGS. 7 through 9 isadded so that the straight traveling state the constant steeringmaintained state can be excluded from the abnormality determination.

As described above, the present invention is not limited to therespective embodiments and so forth. Free structure modifications arepossible without departing from the gist of the present invention.Especially, in each of the preferred embodiments, the present inventionis applied to the power steering apparatus of so-called rack assistancetype. However, the present invention is not limited to this. That is tosay, the present invention is applicable to the power steering apparatusother than rack assistance type, for example, the power steeringapparatus of a column assistance type or of a pinion assistance type. Inthis case, a column shaft and a pinion shaft constituting the steeringmechanism are made of the steel materials. Therefore, there is apossibility of introducing inconveniences due to the rust describedabove. Even if the power steering apparatus of the type described above,the application of the present invention can enjoy the merits of theabnormality determination.

Hereinafter, the invention graspable from the respective preferredembodiments and not described in the claims will be described below.

[claim a] The power steering apparatus as described in claim 1, whereinthe steering load average value calculating circuit stores a newestvalue of the average value of the steering load corresponding value intoa non-volatile memory, when an ignition switch of a vehicle is turnedoff.

According to this invention, when the ignition switch is turned off, thepower supply to the control unit is turned off. However, since thenewest value of the average value of the steering load correspondingvalue is stored in the non-volatile memory, the information before theignition switch is turned off can be utilized at a time of a re-ignition(when the ignition switch is again turned on.

[claim b] The power steering apparatus as claimed in claim a, whereinthe steering load average value calculating circuit calculates theaverage value of the steering load corresponding value on a basis of aninformation of the average value of the steering load correspondingvalue stored in the non-volatile memory and the steering loadcorresponding value after the ignition switch is turned on, when theignition switch of the vehicle is turned on.

According to this invention, the average value of the steering loadcorresponding value can be calculated on a basis of both informationbefore and after the ignition switch is turned on. Thus, a higheraccurate average value calculation can be carried out.

[claim c] The power steering apparatus as claimed in claim b, whereinthe steering load average value calculating circuit calculates theaverage value of the steering load corresponding value by making aweight of the average value of the steering load corresponding valuestored in the non-volatile memory larger than the steering loadcorresponding value after the ignition switch is turned on.

According to this invention, the average value of the steering loadcorresponding value stored in the non-volatile memory is the averagevalue of the steering load corresponding value sampled for a long time.Therefore, by enlarging the weight of the average value during thecalculation of the average value, a more accurate average valuecalculation can be achieved.

[claim d] The power steering apparatus as claimed in claim 1, whereinthe abnormality detection circuit illuminates an alarm light installedin a vehicle when the abnormality detection circuit detects theabnormality of the apparatus.

According to this invention, an illumination of the alarm light informsa driver of the abnormality of the apparatus so as to be enabled to payattention.

[claim e] The power steering apparatus as claimed in claim d, whereinthe control unit outputs the motor command current which has smallervalue than the motor command current when the abnormality of theapparatus is not present, when the abnormality detection circuit detectsthe abnormality of the apparatus.

According to this invention, the steering assistance is not stoppedduring the occurrence of the abnormality but the motor command currentis decreased to perform the steering assistance. Thus, while an abruptincrease of the steering load of the driver is avoided, the abnormalityof the apparatus can be informed to the driver.

[claim f] The power steering apparatus as claimed in claim e, whereinthe control unit calculates the motor command current in a form of agradual decrease of the motor command current, when the abnormalitydetection circuit detects the abnormality of the apparatus.

According to this invention, while the abrupt increase of the steeringload of the driver is avoided, the abnormality of the apparatus can beinformed to the driver.

[claim g] The power steering apparatus as claimed in claim f, whereinthe control unit gradually decreases the motor command current inaccordance with the steering load corresponding value.

According to this invention, a worsening of a steering feeling due tothe increase of the steering load can be suppressed.

[claim h] The power steering apparatus as claimed in claim d, whereinthe control unit zeroes the motor command current after a gradualdecrease of the motor command current.

According to this invention, the motor command current is finallyzeroed. Hence, while the load is gradually decreased, a more accuratepaying attention can become possible. A continuation of the driving bythe driver over a long time in a state in which the abnormality occurscan be suppressed.

[claim i] The power steering apparatus as claimed in claim 1, whereinthe steering mechanism includes a rack bar which axially moves due to arevolution of a steering wheel to steer steerable wheels and the speedreduction mechanism includes a ball-screw mechanism having: a rack barside ball screw groove installed on an outer peripheral side of the rackbar and having a spiral groove shape; a nut annularly installed toenclose the rack bar and rotatably installed with respect to the rackbar; a nut side ball screw groove installed on an inner peripheral sideof the nut, having a spiral groove shape, and constituting a ballcirculation groove together with a steering shaft side ball screw; aplurality of balls installed within the ball circulation groove; and acirculation member installed at an outer side of a radial direction ofthe nut and connecting a one end side of the ball groove and the otherside thereof in order for the plurality of balls to enable a circulationfrom the one end side of the ball circulation groove to the other endside, and a transmission mechanism which transmits the revolution of theelectrically driven motor to the nut.

According to this invention, even if a rust is developed into the ballcirculation groove of the ball-screw mechanism, the development(progress) of the rust can be detected on a basis of the average valueof the steering load corresponding value.

[claim j] The power steering apparatus as claimed in claim 6, whereinthe abnormality detection circuit compares the steering loadcorresponding value when the steering wheel is steering operated withthe specified value to calculate the frequency.

If the frequency of the steering load corresponding value which exceedsthe specified torque including such a situation that the steering loadis not generated as in the straight traveling state, the frequency isrecognized to be low and there is a possibility that the detection ofthe progress of the rust is delayed (late) even if the rust isdeveloped. However, according to this invention, the steering load whenthe steering operation is not carried out is excluded from the frequencycalculation. Thus, a more accurate frequency calculation becomespossible and the development (progress) of rust can be detected at anearly timing.

[claim k] The power steering apparatus as claimed in claim j, whereinthe abnormality detection circuit determines a state in which thesteering wheel is steering operated on a basis of a steering speed, ayaw moment of a vehicle, or a difference of left and right steerablewheel revolution speeds.

According to this invention, the steering operation state can bedetermined on a basis of arbitrary parameters.

[claim l] The power steering apparatus as claimed in claim 6, whereinthe control unit outputs the motor command current which has smallervalue than the motor command current when the abnormality of theapparatus is not present, when the abnormality detection circuit detectsthe abnormality of the apparatus.

According to this invention, the steering assistance is not stoppedduring the occurrence of the abnormality but the motor command currentis decreased to perform the steering assistance. Thus, while an abruptincrease of the steering load of the driver is avoided, the abnormalityof the apparatus can be informed to the driver.

[claim m] The power steering apparatus as claimed in claim l, whereinthe control unit calculates the motor command current in a form of agradual decrease of the motor command current, when the abnormalitydetection circuit detects the abnormality of the apparatus.

According to this invention, while the abrupt increase of the steeringload of the driver is avoided, the abnormality of the apparatus can beinformed to the driver.

EXPLANATION OF SIGNS

-   -   1 . . . steering wheel    -   2 . . . steerable wheel    -   3 . . . steerable wheel    -   18 . . . ECU (Control Unit)    -   19 . . . Electrically driven motor    -   23 . . . torque sensor    -   27 . . . ball-screw mechanism (speed reduction mechanism)    -   39 . . . steering load average value calculating circuit    -   40 . . . abnormality detection circuit    -   Tr . . . steering torque    -   TRr . . . motor command current    -   Ir . . . motor actual current    -   Trav . . . steering torque average value (average value)    -   Trrf . . . specified steering torque value (a specified value)

1. A control unit of a power steering apparatus, the power steeringapparatus comprising: a steering mechanism which steers steerable wheelsin accordance with a steering operation of a steering wheel; a torquesensor which detects a steering torque generated on the steeringmechanism; an electrically driven motor which provides a steering forcefor the steering mechanism; and a transmission mechanism which transmitsa rotational force of the electrically driven motor to the steeringmechanism, the control unit comprising: a steering torque signalreceiving section configured to receive the steering torque signal; amotor command current calculating section configured to calculate amotor command current which drivingly controls the electrically drivenmotor on a basis of the steering torque; and an abnormality detectionsection configured to obtain a signal related to a steering load duringthe steering operation within a predetermined period of time and todetect an abnormality of the power steering apparatus on a basis of anaveraging processed value of the obtained signal.
 2. The control unit ofthe power steering apparatus as claimed in claim 1, wherein theabnormality detection section detects the abnormality of the apparatuson a basis of the averaging processed value of the signal related to thesteering load when the steering wheel is steering operated.
 3. Thecontrol unit of the power steering apparatus as claimed in claim 2,wherein the abnormality detection section determines a state in whichthe steering wheel is steering operated on a basis of a steering speed,a yaw moment of a vehicle, or a difference of left and right steerablewheel revolution speeds.
 4. The control unit of the power steeringapparatus as claimed in claim 1, wherein the abnormality detectionsection stores a newest value of an average value of the signal relatedto the steering load into a non-volatile memory, when a power supply ofthe control unit is turned off.
 5. The control unit of the powersteering apparatus as claimed in claim 1, wherein the abnormalitydetection section illuminates an alarm light of the vehicle, when theabnormality detection section detects the abnormality of the powersteering apparatus.
 6. The control unit of the power steering apparatusas claimed in claim 5, wherein the abnormality detection sectioncalculates the motor command current to become smaller than a case whereno abnormality is present in the power steering apparatus, when theabnormality detection section detects the abnormality of the powersteering apparatus.
 7. The control unit of the power steering apparatusas claimed in claim 6, wherein the abnormality detection sectioncalculates the motor command current to become gradually smaller, whenthe abnormality detection section detects the abnormality of the powersteering apparatus.
 8. The control unit of the power steering apparatusas claimed in claim 7, wherein the abnormality detection sectiongradually reduces the motor command current in accordance with thesignal related to the steering load, when the abnormality detectionsection detects the abnormality of the power steering apparatus.
 9. Thecontrol unit of the power steering apparatus as claimed in claim 5,wherein the abnormality detection section calculates the motor commandcurrent in a form of a gradual decrease of the motor command currentand, thereafter, the motor command current becomes zero, when theabnormality detection section detects the abnormality of the powersteering apparatus.
 10. The control unit of the power steering apparatusas claimed in claim 1, wherein the abnormality detection section detectsthe abnormality of the power steering apparatus on a basis of theaveraging processed value related to the steering load when a steeringspeed is equal to or above a predetermined value.
 11. The control unitof the power steering apparatus as claimed in claim 1, wherein theabnormality detection section does not use the signal related to thesteering load when the steering wheel is bumped in which a steeringangle becomes maximum for a calculation of the averaging process. 12.The control unit of the power steering apparatus as claimed in claim 1,wherein the steering mechanism includes a rack bar which axially movesdue to a revolution of the steering wheel to steer the steerable wheelsand the transmission mechanism includes a steerable wheel axis side ballscrew groove installed on an outer peripheral side of the rack bar andhaving a spiral groove shape; a nut annularly installed to enclose therack bar and rotatably installed with respect to the rack bar; a nutside ball screw groove installed on an inner peripheral side of the nut,having a spiral groove shape, and constituting a ball circulation groovetogether with a steering shaft side ball screw; a plurality of ballsinstalled within the ball circulation groove; and a circulation memberinstalled at an outer side of a radial direction of the nut andconnecting one end side of the ball groove and the other side thereof inorder for the plurality of balls to enable a circulation from the oneend side of the ball circulation groove to the other end side, and atransmission member which transmits the revolution of the electricallydriven motor to the nut.